Swedish Pat. No. 367,792 describes a method of fitting long trailers with load carriers capable of sliding to and fro. In order to slide the load carriers, a longitudinal downward-facing C-section girder or channel member having flat vertical flanges and flat web is fixed centrally to the underside of the load carrier. The vertical flanges has a series of pairs of lugs attached along their upper and lower edges. The trailer chassis is fitted with a backward-facing hydraulic double-acting straight piston servomotor having a fully-closed endplate provided with a lug by means of which it can pivot on a transverse journal so that the piston rod end of the servomotor can pivot in a vertical plane. The free end of the piston rod has a crosspiece arranged to limit the pivoting motion of the servomotor. And, when the crosspiece is in an upper limit position and is being pushed backwards, it is also arranged to engage with a pair of the upper lugs on the C-girder and by means of these to push the load carrier backwards. When the crosspiece is in a lower limit position and is being pulled forward, it is arranged to engage with a pair of the lower lugs of the C-girder and by means of these to pull the load carrier forwards. The ends of the lugs facing away from a mainly vertical striking surface are each bevelled appropriately to function like ratchet teeth so that the crosspiece can slide thereover when pushed in the opposite direction. This makes it possible, by means of a relatively short servomotor, to push the load carrier any required distance.
In the known arrangement referred to above, the hydraulic servomotor is pivoted upwards by a vertically-acting pneumatic piston or bellows servomotor provided under the pivoting end of its cylinder. However, it has been found that such pneumatic piston or bellows servomotors can be subject to failures at temperatures below 0.degree. C., caused by water condensing, from the compressed air supplied thereto, and freezing to ice.
It is accordingly one object of the present invention to provide an arrangement in which the above problem may be reduced or overcome.